A wireless communication network (e.g., employing frequency, time, space, and code division techniques) includes one or more base stations that provide services to a coverage area. A base station can simultaneously transmit multiple data streams for broadcast, multicast, and or unicast services. Communication between base station and mobile terminal can be degraded due to channel variations or interference caused by other base station/terminals, which are communicating within a same coverage area or from other nearby cell or sector. Variations of channel quality associated with changes in interference can be managed by a base station through power control, rate adaptation, or data-packet format reconfiguration, configuration for one or more access terminals. The adjustment relies upon receiving an interference indicator, which is conventionally received over the air interface.
Generally two main challenges of a wireless network operator are to improve network coverage and throughput of the cellular systems. In a cellular wireless system, relay stations (RS) and/or transparent relay stations (T-RS) and/or micro/femto/pico base stations (MBS/FBS/PBS) are often used by the operators to improve the capacity of the system and network coverage. A transparent relay is one that is transparent to the UEs in a broad sense that it cannot be a final destination for any of the information sent from the UE. Likewise, no information can originate from a transparent relay towards the UE. The introduction of RS and MBS/FBS/PBS systems into the network will add to the interference, affecting the user equipments (UE) not served by these components in the system. The quality of communication in a wireless system will depend on the ratio of the received signal to the interference. Interference is of two kind's co-channel interference and neighbor-channel interference. Co-channel interference is due to transmission from communication sources tuned to the same frequency as the operating channel. Neighbor-channel interference results from the communication sources using channels near the operating channel in the operating spectrum. All these effects lower the throughput of the system.
Further in a cellular wireless system, relay stations (RS) and micro/femto/pico base stations (MBS/FBS/PBS) are often used by operators/subscribers to improve capacity and/or coverage. Also in-band backhauling of BS-RS link often creates additional interference to the user equipment (UE) in the system thereby lowering the system throughput. Traditionally, interference management is done by static partitioning of resources between RS/MBS/FBS/PBS and BSs, which results in underutilization of resources as the reuse factor will be less than one.
Traditionally, static resource partitioning techniques have been adopted for interference management where the RSs, MBS/FBS/PBSs and the serving BS in a cell are pre-allocated orthogonal resources. Hereafter, serving BS shall refer to any entity located in the core network including, but not limited to BS, Femto Gateway or the core network itself. Such fixed or semi-static orthogonal resource allocation schemes are relatively easy to implement, but require fairly accurate prior estimates of the expected traffic load on RSs and MBS/FBS/PBSs. In the absence of this information, under-utilization or congestion of resources is inevitable.
The other approach is to schedule all RS/MBS/FBS/PBSs in a centralized manner at the BS by dynamic allocation of resources to RS/MBS/FBS/PBSs. But the major drawbacks associated with this mode of operation are increased control overheads (both signaling and implementation) and the time delay associated with it. This is because, BS sends the resource allocation information called RS-MAP to each RS in every frame, and each RS based on the RS-MAP, RS will transmit data to its associated UEs. Each step in the process such as deciding resource allocation for RS at BS, transmission and reception of RS-MAP and resource allocation at RS based on RS-MAP adds complexity and time delay.
RS support in both IEEE 802.16m and LTE-A are expected to use a distributed scheduling mode in addition to centralized scheduling. However, in the current form of distributed approach, the schedulers at each RS, MBS/FBS/PBS schedule their associated UEs independently with transmit power level information, MIMO schemes, modulation, frequency/resource allocation and code rates decided by RS without accounting for the interference experienced by the UEs in the system. This distributed scheduling scheme, though simple to implement, will result in increased interference thereby significantly reducing system throughput.
In addition, the standards support various interference mitigation techniques such as using Fractional Frequency Reuse (FFR), Advanced Antenna Technologies, Power Control, Scheduling etc., and have defined management messages. For example in IEEE 802.16m, messages like AAI_MOB_REQ and AAI_MOB-REP sent by the UE and AAI_MOB-RSP sent by the BS along with the AAI_NBR_ADV and other related messages are expected to be used by the UE for the purpose of scanning and reporting the measured signal parameters such as received signal strength indicator (RSSI), carrier to interference plus noise ratio (CINR) etc. with respect to a set of neighboring BS/RS/MBS/FBS/PBS to the serving BS for deciding on the suitability of the set of BS/RS/MBS/FBS/PBS as targets for Handover (HO).